1. Field of the Invention
The invention relates to a private branch exchange comprising a line card, which card includes a plurality of interfaces for accommodating data from incoming subscriber lines in standard output frames, these frames comprising subscriber data and control data.
The invention further relates to a line card to be used in such a private branch exchange.
2. Discussion of the Related Art
A known interface to be used on a line card in a private branch exchange is the ISAC.RTM.-S interface from Siemens. A manual in which this interface is described is called "ICs for Communications, ISDN Subscriber Access Controller, ISAC.RTM.-S, PEB 2085". This manual will further be referred to as ISAC.RTM.-S manual. The ISAC.RTM.-S inserts data of incoming subscriber lines into standard output frames which are further filled up with control data. These standard output frames are switched to a system bus, the so-called IOM.RTM.02 bus. This bus conveys these data to other system components present on the line card. The IOM.RTM.-2 bus has a standard system frame comprising 8 channels accommodating each exactly one standard output frame of an ISAC.RTM.-S interface. By programming the ISAC.RTM.-S interfaces there may be determined which channel is assigned to which interface. The standard output frames comprise data which cannot be used in certain types of private branch exchanges and are thus redundant. This means that the frame is not filled efficiently. Each IOM.RTM.-2 bus is basically only suitable for processing the data coming from 8 interfaces.